Leaf Developmental Stage Influences Primary Metabolite Profiles
To identify shifts in metabolism associated with leaf development,
untargeted GC/MS analysis of a range of polar and non-polar compounds
was undertaken. A total of 107 chromatographic features were resolved
representing 36 non-polar and 71 polar components. Thirty of the
features were unidentified with the remaining 77 identified based on
their relative retention times and mass spectra. Only 26 components
exhibited significant differences in abundance dependent on leaf section
of which 19 were present in the polar fraction and 7 in the non-polar
fraction (Table S7). Twenty of these compounds were identified
comprising sugars, organic acids, amino acids, fatty acids and alcohols
(Fig. 7). A minor unoximated fructose peak exhibited a decline from leaf
base to tip however, this represented less than 10% of the total
fructose pool and neither of the major oximated peaks exhibited
significant change (Table S7). Mannitol exhibited a similar change in
abundance to the unoximated fructose peak while galactose was least
abundant in the leaf base but higher in the mid and tip regions (Fig.
7). The TCA cycle organic acids fumarate and succinate were most highly
abundant in the base and mid regions of the leaf but declined
dramatically in the leaf tip perhaps due to a redirection of flux into
amino acids, the majority of which exhibited an increase as the leaf
aged (Fig.7). Significantly, although both glycine and serine increased
as the leaf aged, glycine increased to a much greater extent meaning a
higher glycine/serine ratio indicative of increased photorespiration
(Novitskaya, Trevanion, Driscoll, Foyer, & Noctor, 2002) from leaf base
to tip. Of the four lipophilic compounds that exhibited significant
changes in abundance, all increased in the leaf tip relative to the leaf
basal region.